One of several reasons for this high uncertainty is the complexity of determining the cooling effects of aerosols, which reflect sunlight back to space, and can also seed cloud formation. According to the authors, "Aerosols counteract part of the warming effects of greenhouse gases, mostly by increasing the amount of sunlight reflected back to space. However, the ways in which aerosols affect climate through their interaction with clouds are complex and incompletely captured by climate models." "Recent advances have led to a more detailed understanding of aerosol-cloud interactions and their effects on climate, but further progress is hampered by limited observational capabilities and coarse-resolution climate models."

The huge uncertainties with respect to clouds, aerosols, solar amplification mechanisms, ocean oscillations, and natural variability all make a mockery of the IPCC claim of increased confidence as its climate models increasingly diverge from temperature observations....